U.S. patent number 3,790,998 [Application Number 05/195,350] was granted by the patent office on 1974-02-12 for method of making a lamp with oscillating filament.
This patent grant is currently assigned to Duro-Test Corporation. Invention is credited to Rudolph Kaufman, Wolfgang E. Thouret.
United States Patent |
3,790,998 |
Kaufman , et al. |
February 12, 1974 |
METHOD OF MAKING A LAMP WITH OSCILLATING FILAMENT
Abstract
A method is disclosed for selecting the proper filament length
in an incandescent lamp designed for operation from a source of
alternating current of a given frequency, the lamp having a magnet
producing a magnetic field which reacts with the current through
the filament to cause the filament to oscillate. The length of the
filament is selected in accordance with the frequency of the
operating current to enhance the probability of the filament
oscillating.
Inventors: |
Kaufman; Rudolph (Bronxville,
NY), Thouret; Wolfgang E. (Verona, NJ) |
Assignee: |
Duro-Test Corporation (North
Bergen, NJ)
|
Family
ID: |
22721091 |
Appl.
No.: |
05/195,350 |
Filed: |
November 3, 1971 |
Current U.S.
Class: |
445/3; 313/315;
313/160; 315/267 |
Current CPC
Class: |
H01K
3/305 (20130101) |
Current International
Class: |
H01K
3/30 (20060101); H01K 3/00 (20060101); H01j
009/18 (); H01j 009/42 () |
Field of
Search: |
;313/160,315 ;315/267
;29/593,25.18,25.13,25.14 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saalbach; Herbert K.
Assistant Examiner: Rosenberger; Richard A.
Attorney, Agent or Firm: Darby & Darby
Claims
What is claimed is:
1. The method of producing incandescent lamps with oscillating
filaments for operation from a source of electric current of a
given frequency comprising the steps of
providing a number of envelopes of the same type and a number of
permanent magnets having substantially the same magnetic field
strength,
providing a batch of a number of filaments having substantially the
same chemical and physical characteristics, including length, from
having been manufactured under substantially the same manufacturing
conditions,
taking at least one sample from said batch of filaments,
determining the optimum length of the sample filament taken from
the batch for producing oscillation when operated at said given
frequency with one of said number of magnets in a said
envelope,
trimming the lengths of the other filaments of said batch to said
optimum length as required, and
mounting each of said other filaments in one of said envelopes with
a respective one of said number of magnets.
2. The method of claim 1 wherein said determining step includes
taking a sample number of filaments from said batch of filaments,
trimming the filaments of the sample number to different sizes,
then operating said sample number of filaments in respective lamps
at said given frequency to determine which filament length has the
best oscillating characteristics.
3. The method of claim 2 further comprising the step of trimming
all of the filaments of the batch to the same length as the
filament having the best oscillating characteristics.
Description
This invention relates to incandescent lamps and more particularly
to incandescent lamps having an oscillating filament.
Incandescent lamps which operate on alternating current and have a
magnet either inside or outside of the lamp envelope for producing
a magnetic field to react with the current flowing through the lamp
filament for the purpose of making the lamp filament oscillate are
known in the art. Such lamps are disclosed in U. S. Pat. Nos.
3,237,053, 3,548,255 and 3,549,946.
Lamps of the foregoing type normally use a carbon filament. Carbon
filaments are well known in the art and there are many methods for
producing these filaments and for aging these filaments prior to
operating in the lamp. Heretofore, filaments for these lamps were
made primarily on a basis such that the filament would have a
length sufficient, when formed to the desired shape, so as to
produce a desired visual effect when oscillating.
Because of variances from batch to batch in the manufacturing
procedures for carbon filaments nominally made to the same
specifications, differences are present in the final filament
structures. These differences are due to small variations in the
chemical composition of the filaments, for example, the percentage
of binder material, impurities, etc. Other variances occur due to
such factors as the pressure applied to form the filament, the time
and temperature used for baking out the filament, and other
factors. All of these contribute to differences in the filaments of
various batches. When these filaments are used in an application
where they do not have to oscillate, the differences are
insignificant or meaningless.
In manufacturing lamps of the type having an oscillating carbon
filament, a major problem encountered is a high number of rejects
due to filaments which will not oscillate or which have a limited
degree of oscillation insufficient for consumer acceptance. In a
typical case, using the same manufacturing procedure (e.g. same
method of filament aging, same degree of vacuum, same outgassing,
etc.) and the same types of components (e.g. same field strength
magnets, same envelopes) for making a number of lamps, the
filaments of some lamps will oscillate while others will not. The
reason for this has heretofore been unexplained.
In accordance with the subject invention, applicants have found
that a direct relationship exists in manufacturing a lamp of the
type having an oscillating carbon filament between the frequency of
the alternating current applied to the lamp and the length of the
filament, all other factors of manufacturing being equal or
substantially equal. That is, from a given batch of carbon
filaments having the same, or substantially the same,
characteristics, which normally occurs because the filaments of the
batch are all manufactured at the same time, an optimum length
exists for the filaments so that the largest number of filaments of
the batch will oscillate at a given frequency. Therefore, the
present invention provides an incandescent lamp with an oscillating
filament in which the filament is selected to have an optimum
length to ensure the best probability that the largest number of
filaments in the same batch will oscillate.
It is therefore an object of the present invention to provide an
incandescent lamp with an oscillating filament and the method of
making the same.
A further object is to provide an incandescent lamp with an
oscillating filament in which the filament is selected to have a
predetermined size relationship with respect to the frequency of
alternating current supplied to the lamp.
An additional object is to provide an incandescent lamp having an
oscillating carbon filament in which the selection of the filaments
on the basis of length and other characteristics increases the
productivity yield .
Other objects and advantages of the present invention will become
more apparent upon reference to the following specification and
annexed drawings, in which:
FIG. 1 is an elevational view of a lamp made in accordance with the
invention, and
FIG. 2 is a view of the lamp of FIG. 1 turned by 90.degree..
Referring to FIG. 1, there is shown an incandescent lamp which
includes an envelope 10 of a suitable translucent material, such as
glass. The envelope 10 is sealed by a base 12 having the usual
electrical contacts 13 and 14 thereon through which alternating
current from a suitable source (not shown) is supplied to the lamp.
The base covers a stem 16 used for exhaust purposes. The upper
portion of the stem is shown. All of the foregoing structure is
conventional.
The stem 16 has a pair of lead wires 18 and 19 passing therethrough
which are attached within the base to the electrical contacts of
the base member. The ends of the lead wires 18, 19 extend above the
stem 16 and a filament 20 is connected thereto at the mounting
points 18a and 19a. This mounting can be accomplished by a suitable
adhesive of conductive material. The filament 20 is preferably of
carbon material which has been bent into a desired shape such as
the modified loop shown. The ends of the filament 20 are mounted to
the lead wires at points 18a, 19a by any suitable means, for
example a conductive adhesive.
A support pin 25, which can be of conductive or insulating
material, has one end embedded in the stem. A permanent magnet 30,
for example of ALNICO or any other suitable ferromagnetic material
or alloy thereof, is mounted at the top end of pin 25. The magnet
can have any desired shape, the only requirement being that it
produces adequate flux to interact with the current of the filament
to cause the filament to oscillate. As shown, the longitudinal axis
of the magnet is generally transverse to the plane of the loop of
the filament so that the lines of flux are also transverse to the
plane of the filament 20. However, this orientation is not
absolutely necessary and there can be an angular orientation
between the longitudinal axis of the magnet and the plane of the
loop of less than 90.degree..
In operation, alternating current is supplied to the lamp of FIG. 1
and flows through the filament 20. The interaction of the lamp
current and the magnetic field from magnet 30 produces a force in
accordance with classical electromagnetic theory. This force causes
the filament to oscillate to and fro on the mounts 18a, 19a as the
direction of the current flowing through the filament
alternates.
In accordance with the invention, it has been found that the length
of the carbon material in the filament loop 20, that is, between
the points of connection 18a and 19a to the lead wires 18 and 19,
is critical with respect to the oscillation of the filament, all
other conditions of manufacture and selection of components being
equal or substantially equal. That is, assuming filament material
of the same composition made by the same manufacturing process, the
total length of the filament between the points of connection 18a,
19a with the lead wires 18, 19 will determine whether or not the
filament will oscillate at a given frequency of alternating current
applied to the lamp. This fact has not previously been recognized.
Generally, in ordering filaments from a commercial manufacturer, a
general overall length of filament, with tolerances, is specified.
The filaments are manufactured in a U-shape and they are used in
the lamps without any additional trimming of the filament length
after the original U-shape has been modified to a predetermined
loop configuration. In general, a high number of rejects have been
encountered, that is, the filaments of some batches will not
oscillate or will oscillate very poorly and will not be acceptable
to a customer.
In accordance with the present invention, the lengths of the
filament (from points 18a to 19a) are "trimmed" or selected to have
a length which will be proper for the filament to oscillate at the
operating frequency applied to the lamp. In practice, the length of
the filaments are selected to include the portions used for
mounting (that is, the inactive portion which is either attached to
lead wires 18, 19 or extend beyond the lead wires) since the
mounting of all filaments is carried out in the same way using the
same overall length of filament material.
One way of determining the proper length is to start with a batch
of carbon filaments which have been made at the same time and which
have been cut roughly to the same overall length. The fact that the
filaments were manufactured at the same time ensures that they
should have the same, or substantially the same, characteristics.
Sets of filaments (e.g. six filaments to a set) are then made up
from this batch for test purposes, the difference in the filaments
from one set to the next being only in length. Sets of lamps are
used instead of individual lamps to reduce the possibility of error
due to various causes. For example, the filaments of the different
sets can differ by one millimeter, or one-half millimeter, in
length.
The sets of filaments which are so trimmed are then mounted in
lamps which have the same components. These lamps are processed to
completion in the same way and the finished lamps are then operated
from a source of alternating current of the same frequency for
which the lamps are designed. From the total group of lamps, the
lamps of one set will exhibit the best overall oscillating
characteristics and/or have the greatest number oscillate. The
filaments of this set are all of the same length.
After the optimum length of the filaments for the particular batch
has been determined, the remaining filaments in the batch are cut
to this optimum length. That is, the filaments of the batch are all
cut so that their lengths between mounting points 18a and 19a will
be the same.
It has been found that filaments obtained from the same
manufacturer and made to the same specifications will differ
considerably insofar as their ability to oscillate is concerned.
The filaments often have to be trimmed by as much as approximately
.+-.2 percent of their overall manufactured length to make the
filaments ocillate.
By utilizing the principles of the subject invention, the
manufacturing yield of lamps of the foregoing type has been raised
by a considerable degree.
It should be understood that filaments trimmed to a given length to
oscillate when operated by current of one frequency will not
operate with current of a frequency which is considerably
different. For example, filaments cut for oscillation at 60Hz will
not operate when the current is 50Hz, or even 55Hz. Since higher
frequency operating currents normally result in lamps with shorter
filament lengths for successful oscillation, if lamps for use with
different frequencies are being manufactured, the filaments for the
lower frequency lamps should be selected first since these are
longer and can be used for higher frequency operation if trimmed
down too far.
While the illustrative embodiment of the invention shows magnet 30
inside of the lamp envelope, it should be understood that the
magnet can be mounted outside of the envelope, provided the
magnet's flux strength is sufficient to produce filament
oscillation.
A rigorous mathematical treatment for the dependence of length of
the filaments needed for oscillation has not been made. However, as
pointed out above, it is believed that as between filaments
manufactured to the same specifications but at different times, the
differences in the ability to oscillate occur due to variances in
chemical composition or processing factors which would be
considered to be minute or even insignificant when the same
filaments are used in applications where they do not have to
oscillate. These variances can be overcome and the filaments made
to oscillate, or have the greatest probability of oscillating, by
trimming them to the appropriate lengths for the particular batch
of filaments.
* * * * *